Large-scale electrochemical synthesis of SnO2 nanoparticles

Tin oxide nanoparticles were synthesized by electrochemical oxidation of a tin metal sheet in a nonaqueous electrolyte containing NH4F. The as-prepared nanoparticles were then thermally annealed at 700 C for 6 h. The resulting particles were characterized by a variety of experimental techniques, including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman, UV-visible, and photoluminescence (PL) spectroscopy. The XRD patterns clearly showed that the amorphous phase of the as-synthesized SnO2 particles was transformed into a rutile-type crystalline structure after thermal treatment; and from the line broadening of the XRD peaks, the average size of the annealed particles was found to be 15.4, 12.5, 11.8 nm for the particles initially synthesized at 20, 30, and 40 V, respectively. Consistent results were also observed in HRTEM measurements which showed clear crystalline lattice fringes of the calcined nanoparticles, as compared to the featureless profiles of the as-produced counterparts. In Raman spectroscopic studies, three dominant peaks were observed at 480, 640, and 780 cm which were ascribed to the E1g, A1g, and B2g Raman active vibration modes, respectively, and the wavenumbers of these peaks blue-shifted with decreasing particle size. Additionally, a broad strong emission band was observed in room-temperature photoluminescence measurements. Introduction Transition-metal oxide nanomaterials, such as ZnO, TiO2, WO3, and SnO2, have attracted extensive research interests owing to their unique physical and chemical properties and diverse potential applications in optical and electronic fields. Of these, tin oxide (SnO2) with the rutile structure is a promising functional n-type semiconductor material with a wide band-gap (Eg = 3.65 eV at 300 K), which has been used extensively in energy storage and conversion (for instance, solar cells and lithium ion batteries) [1–3], catalysis [4–6], gas sensors [7–11], transparent conducting electrodes [12], and optoelectronic devices [13–15]. To date, a wide variety of SnO2 nanomaterials with interesting structures and properties have been prepared, such as nanoparticles [16–19], nanorods [20–22], nanotubes [3], nanowires [9, 23], nanobelts [8, 24, 25], and hollow spheres [26, 27]. The typical synthetic approaches entail sol–gel processes [2, 11, 28, 29], vapor-liquid-solid (VLS) growth [25, 30, 31], chemical vapor deposition [32– 34], sputtering [35, 36], and solution phase growth [7, 37– 39]. In these, high temperature and/or vacuum are generally required, along with complicated preand postsynthesis processing. For instance, in most of these strategies, surfactants or organic polymers are used to control the dimensions and morphologies of the SnO2 nanomaterials. Yet, prior to practical applications, these organic impurities typically have to be removed, and such processing may lead to complication of the particle size, surface area, and stability of the particles. In the traditional solution phase growth methods [7, 37–39], the by-products may also compromise the material purity. Thus, it is important to develop an effective strategy to prepare pure tin oxide nanomaterials with high efficiency and under mild conditions from the viewpoints of both fundamental W. Chen D. Ghosh S. Chen (&) Department of Chemistry and Biochemistry, University of California, 1156 High Street, Santa Cruz, CA 95064, USA e-mail: [email protected] 123 J Mater Sci (2008) 43:5291–5299 DOI 10.1007/s10853-008-2792-x